Pneumatic tire having excellent steering stability

ABSTRACT

A pneumatic tire has a block pattern of a tread defined by a plurality of circumferential grooves extending in a circumferential direction of the tread and a plurality of lateral grooves each extending across the circumferential grooves and tread ends, wherein specified chamfered face, sipe or fine groove is formed in each block of all block rows to improve a self-aligning torque in the high-speed running of a vehicle.

This is a Divisional of Application No. 09/482,011 filed Jan. 13, 2000now U.S. Pat. No. 6,405,772; the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pneumatic tire having particularly animproved steering stability in the high-speed running of a vehicle byincreasing a self-aligning torque of the tire.

2. Description of Related Art

In the running of the vehicle, the steering stability is largelyaffected by disturbances such as road surface state, wind and the like,which becomes serious as the vehicle speed is increased. In theconventional pneumatic tire, however, examinations on the shape of theblock, formation of sipe and the like are not made for sufficientlysatisfying the steering stability in the high-speed running of thevehicle.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide pneumatic tiresadvantageously improving the steering stability in the high-speedrunning by directly increasing self-aligning torque of the tire throughblock, sipe and the like as a result of various studies with respect tothe block shape and formation of sipe or fine groove therein.

According to a first aspect of the invention, there is the provision ofin a pneumatic tire having a block pattern of a tread defined by aplurality of circumferential grooves extending in a circumferentialdirection of the tread and a plurality of lateral grooves each extendingacross the circumferential grooves and tread ends, the improvementwherein each block in an outermost block row in a widthwise direction isprovided on its leading edge portion with a chamfered face graduallydecreasing a height of the block toward a leading edge, and each blockin the other block rows is provided on its trailing edge portion with achamfered face gradually decreasing a height of the block toward atrailing edge, and a length of a chamfered face forming region is notmore than ⅓ of a circumferential length of the block.

When a slip angle is applied to this pneumatic tire, the block in theoutermost block row located opposite to the applying direction of theslip angle contacts with ground at a large area under a large loadingand hence a force in a forward direction produced in the leading of theblock is weakened by the chamfered face formed on the leading edgeportion of the block to relatively create a large force backward to aforward rotating direction of the tire as compared with the block of theother block row provided on the trailing edge portion with the chamferedface, whereby restoring moment or self-aligning torque is caused in theground contact region of the tread. As a result, even when the tire issubjected to disturbance or the like, it is possible to smoothly andrapidly return the tire in a running direction of the vehicle.Therefore, the excellent steering stability can be realized even in thehigh-speed running of the vehicle.

In a preferable embodiment of the first aspect, the chamfered face isformed in a region corresponding to not more than ⅓ of thecircumferential length of the block, preferably not less than {fraction(1/10)} thereof, whereby the ground contact area of the block issufficiently ensured.

When the length of the chamfered face forming region exceeds ⅓ of acircumferential length of the block, the ground contact area of theblock lowers and hence cornering power important for improving thesteering stability is lacking, while when it is less than {fraction(1/10)}, the effect by the formation of the chamfered face is actuallypoor.

In another preferable embodiment of the first aspect, a height of thechamfered face forming region is not more than ⅓ of a height of theblock, preferably not less than {fraction (1/10)} thereof. In this case,a big self-aligning torque can be created to effectively ensure theimprovement of the steering stability during the high-speed running.When the height exceeds ⅓, the ground contact area is decreased too muchand hence the cornering power is decreased to cause a fear of degradingthe steering stability, while when it is less than {fraction (1/10)},the actual effect is lacking.

In the other preferable embodiment of the first aspect, the chamferedface is a curved face convexly extending outward in a radial directionof the tire. In this case, the ground contact pressure is uniformized tocontrol the lowering of the cornering power as compared with the case offorming a flat chamfered face or the like.

According to a second aspect of the invention, there is the provision ofin a pneumatic tire having a block pattern of a tread defined by aplurality of circumferential grooves extending in a circumferentialdirection of the tread and a plurality of lateral grooves each extendingacross the circumferential grooves and tread ends, the improvementwherein a plurality of sipes each extending in a widthwise direction ofthe tread and being symmetry with respect to a line segment passingthrough a center of the block in the circumferential direction of thetread are formed in each block of the block rows so as to graduallychange lengths of these sipes from an end of the block in thecircumferential direction toward the other end thereof, and the sipes ineach block of an outermost block row become long at a leading side ofthe block and short at a trailing side thereof, and the sipes in eachblock of the other block rows become long at a trailing side of theblock and short at a leading side thereof.

In this tire, each sipe formed in each block and extending in thewidthwise direction of the tread can naturally develop an excellentwater film cutting performance under its edge action but alsoparticularly decreases a block rigidity at the leading edge portion ineach block of the outermost block row. As a result, when a slip angle isapplied to the tire, a force in a forward direction produced in theleading of the block is decreased to relatively increase a force in abackward direction, while a block rigidity at a trailing edge portion isdecreased in each block of the other block rows to relatively increase aforce in a forward direction. Even in this case, the self-aligningtorque can effectively be increased based on force couple in the groundcontact region of the tread, whereby the excellent steering stabilitycan be realized during the high-speed running of the vehicle.

In a preferable embodiment of the second aspect, both ends of each sipein each block are terminated in the block, whereby the excessivelowering of the block rigidity is prevented to control the occurrence ofuneven wear.

According to a third aspect of the invention, there is the provision ofin a pneumatic tire having a block pattern of a tread defined by aplurality of circumferential grooves extending in a circumferentialdirection of the tread and a plurality of lateral grooves each extendingacross the circumferential grooves and tread ends, the improvementwherein each block in all block rows is provided with a single finegroove extending in a widthwise direction of the tread across the block,and the fine groove formed in each block of an outermost block row islocated in a leading edge portion of the block and the fine grooveformed in each block of the other block rows is located in a trailingedge portion of the block.

Even in this tire, a block rigidity in each block of the outermost blockrow is lower at the leading edge portion than at the trailing edgeportion, while a block rigidity in each block of the other block rows islower at the trailing edge portion than at the leading edge portion, sothat the self-aligning torque can be increased to bring about theimprovement of the steering stability during the high-speed runninglikewise the previously mentioned tires.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 a is a schematically partial developed view of a first embodimentof the tread pattern according to the invention;

FIG. 1 b is a diagrammatically section view of a block taken along aline Ib—Ib of FIG. 1;

FIG. 1 c is a diagrammatically section view of a block taken along aline Ic—Ic of FIG. 1;

FIG. 2 is a schematically partial developed view of a second embodimentof the tread pattern according to the invention; and

FIG. 3 is a schematically partial developed view of a third embodimentof the tread pattern according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1 is shown a first embodiment of the tread pattern according tothe invention, wherein FIG. 1 a is a schematically partial developedview of the tread pattern, and FIGS. 1 b and 1 c are diagrammaticallysection views of blocks in a circumferential direction of the treadtaken along lines Ib—Ib and Ic—Ic, respectively.

Moreover, an inner structure of the tire is the same as in the generallyused radial tire. Such an inner structure itself is not directly relatedto the invention, so that the illustration of the inner structure isomitted.

In the illustrated embodiment, a center block row 4 located on anequator of the tire, shoulder block rows 5 located at both outermostsides of a tread portion and middle block rows 6 located between thecenter block row and the shoulder block row are defined on a surface ofa tread by four circumferential grooves 1, 2 extending straightforwardin a circumferential direction of the tread and symmetrically locatedwith respect to the equator of the tire, both tread side ends E and aplurality of lateral main grooves 3 extending across thesecircumferential grooves 1, 2 and substantially in a directionperpendicular thereto.

When such a tread portion is rotated upward as shown by an arrow A inFIG. 1 a, a chamfered face 8 is formed on a leading edge portion of eachshoulder block 7 in the shoulder block row 5 so as to gradually decreasea height of the block toward a leading edge 7 a as seen from a sectionview of FIG. 1 b, wherein a length 1 of a forming region for thechamfered face 8 is made not more than ⅓ of a circumferential length Lof the shoulder block 7. Preferably, the chamfered face 8 is a curvedface convexly extending outward in a radial direction of the tire.

Furthermore, it is favorable that a height h of the forming region forthe chamfered face 8 is made not more than ⅓ of a height H of theshoulder block 7, whereby it is possible to effectively ensure theimprovement of the steering stability as previously mentioned.

In blocks 9, 10 of the other block rows 4, 6, as shown in FIG. 1 cillustrating a center block 9, a chamfered face 11 is formed on atrailing edge portion of the block so as to gradually decrease a heightof the block toward a trailing edge 9 a, wherein a forming region forthe chamfered face 11 is made not more than ⅓ of a circumferentiallength of the block 9 likewise the above case. This is true in eachblock 10 of the middle block row 6.

Even in this case, the chamfered face 11 is favorable to be a curvedface convexly extending outward in the radial direction of the tire anda height of a forming region therefor is favorable to be not more than ⅓of a block height.

When the blocks 7, 9 and 10 are chamfered as mentioned above, if acertain slip angle is applied to the tire, the blocks 7 strongly andlargely contact with ground at a side opposite to the slip angle appliedside as compared with the blocks 9, 10 mainly based on relativedifference between the forming positions of the chamfered faces 8, ii inthe blocks, whereby the self-aligning torque of the tire canadvantageously be increased.

In FIG. 2 is shown a second embodiment of the tread pattern according tothe invention, wherein a center block row 4 located on an equator of thetire, shoulder block rows 5 located at both outermost sides of a treadportion and middle block rows 6 located between the center block row andthe shoulder block row are defined on a surface of a tread by fourcircumferential grooves 1, 2 extending straightforward in acircumferential direction of the tread and symmetrically located withrespect to the equator of the tire, both tread side ends E and aplurality of lateral main grooves 3 extending across thesecircumferential grooves 1, 2 and substantially in a directionperpendicular thereto likewise the case of FIG. 1 and a plurality ofsipes 12 each extending in a widthwise direction of the tread and beingsymmetry with respect to a line segment passing through a center of theblock in the circumferential direction of the tread are formed in eachof the blocks 7, 9, 10 so as to gradually change lengths of these sipesfrom an end of the block in the circumferential direction toward theother end thereof. The sipes 12 in the shoulder block 7 become long at aleading side of the block 7 and short at a trailing side thereof, andthe sipes 12 in each of the center blocks 9 and middle blocks 10 becomelonger at a trailing side of the block than at a leading side thereof.

In the illustrated embodiment, both ends of all sipes 12 in each blockare terminated in the block.

Moreover, the term “sipe” used herein means a narrow groove havinggenerally an opening width of about 0.2-0.4 mm, wherein opposed groovewalls of the sipe contact with each other in a ground contact regionduring the running of the tire under loading.

When a certain slip angle is applied to this tire, force directingbackward in a running direction of the tire is created in the shoulderblock 7 subjected to a large load based on the difference of theextending lengths of the sipes 12 between mutual blocks to cause coupleforce in the ground contact region of the tread, whereby the increase ofthe self-aligning torque in the tire can be realized.

In FIG. 3 is shown a third embodiment of the tread pattern according tothe invention, wherein each of the blocks 7, 9, 10 in all the block rows4, 5, 6 formed by the same method as in the first and second embodimentsis provided with a single fine groove 13 extending in a widthwisedirection of the tread across the block. The forming position of thefine groove 13 is a leading edge portion in the shoulder block 7 and atrailing edge portion in the other blocks 9, 10.

The term “fine groove” used herein means a groove having an openingwidth of about 0.5-3 mm.

Moreover, it is favorable that the fine groove 13 is located apart froman edge of the block near to the fine groove within a range of 0.1-0.35times the length of the block in the circumferential direction forsimultaneously establishing the steering stability and the resistance touneven wear.

According to this tire, the increase of the self-aligning torque can beattained under substantially the same function of the blocks as shown inFIG. 2 based on the difference of the fine groove forming positionbetween the mutual blocks.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

EXAMPLE 1

There is provided a pneumatic tire having a tire size of 195/60R15 88Hand a tread pattern shown in FIG. 1 a, wherein a belt is comprised oftwo cross belt layers, cords of which layers are crossed with each otherat a cord angle of 20° with respect to an equator of the tire and has awidth of about 150 mm, and each block has a height of 5 mm and a lengthin circumferential direction L of 18.9 mm, and a chamfered face formedin a shoulder block has a forming region length 1 of 6 mm and a formingregion height h of 1.2 mm. This tire is mounted onto a rim of 6J andinflated under an air pressure of 220 kPa and rotated on a drum testingmachine at a speed of 60 km/h under a load of 4067 N while applying aslip angle of 3° to measure a self-aligning torque.

For the comparison, there is provided a comparative tire wherein thechamfered face formed in all of the blocks is the same as formed in thecenter block and the middle block shown in FIG. 1. The self-aligningtorque of this comparative tire is measured in the same manner asmentioned above.

When the self-aligning torque is represented by an index on the basisthat the comparative tire is 100, the index value of the example tire is101, so that the self-aligning torque can be increased by about 1%.

EXAMPLE 2

There is provided a tire having the same structure as in Example 1except that the tire has a tread pattern shown in FIG. 2, wherein foursipes having an opening width of 0.3 mm are formed in each of all blocksand lengths of the sipes in each of shoulder blocks located at aposition apart from a tread end within 0.15 times a ground contact widthof a tread successively change into 20 mm, 14 mm, 8 mm and 4 mm from aleading edge of the block and lengths of the sipes formed in the otherblocks successively change into 20 mm, 14 mm, 8 mm and 4 mm from atrailing edge of the block. The self-aligning torque of this tire ismeasured in the same manner as in Example 1.

For the comparison, there is provided a comparative tire wherein foursipes having a length of 10 mm are formed in all of the blocks.

When the self-aligning torque is represented by an index on the basisthat the comparative tire is 100, the index value of the example tire is100.5, so that the self-aligning torque can be increased by about 0.5%.

EXAMPLE 3

There is provided a tire having the same structure as in Example 1except that the tire has a tread pattern shown in FIG. 3, wherein eachof all the blocks is provided with a fine groove having an opening widthof 2 mm and the fine groove formed in the shoulder block is locatedapart from a leading edge of the block by ⅕ of a length of the block ina circumferential direction and the fine groove formed in the otherblocks is located apart from a trailing edge of the block by ⅕ of alength of the block in the circumferential direction.

For the comparison, there is provided a comparative tire wherein thefine groove formed in all the blocks is located in a positioncorresponding to ½ of the length of the block in the circumferentialdirection.

When the self-aligning torque is represented by an index on the basisthat the comparative tire is 100, the index value of the example tire is101, so that the self-aligning torque can be increased by about 1%.

As mentioned above, according to the invention, the self-aligning torqueof the tire can effectively be increased to advantageously improve thesteering stability in the high-speed running of the vehicle.

1. A pneumatic tire comprising a block pattern of a tread defined by aplurality of circumferential grooves extending in a circumferentialdirection of the tread and a plurality of lateral grooves each extendingacross the circumferential grooves and tread ends, wherein a pluralityof sipes each extending in a widthwise direction of the tread and beingin symmetry with respect to a line segment passing through a center ofthe block in the circumferential direction of the tread are formed ineach block of the block rows so as to gradually change lengths of thesesipes from an end of the block in the circumferential direction towardthe other end thereof, and the sipes in each block of outermost blockrows become long at a leading side of the block and short at a trailingside thereof, and the sipes in each block of inner block rows betweenthe outermost block rows become long at a trailing side of the block andshort at a leading side thereof.
 2. A pneumatic tire according to claim1, wherein both ends of each sipe in each block are terminated in theblock.
 3. A pneumatic tire comprising a block pattern of a tread definedby a plurality of circumferential grooves extending in a circumferentialdirection of the tread and a plurality of lateral grooves each extendingacross the circumferential grooves and tread ends, wherein each block inall block rows is provided with a single fine groove extending in awidthwise direction of the tread across the block, and the fine grooveformed in each block of outermost block rows is located in a leadingedge portion of the block and the fine groove formed in each block ofinner block rows between the outermost block rows is located in atrailing edge portion of the block.